1. Field of the Invention
The present invention relates to improvements in a photoelectrical encoder wherein a physical quantity is detected through brightness obtained by moving two optical gratings relative to each other.
2. Description of the Prior Art
The conventional photoelectrical encoders each have been of such an arrangement that rays are radiated from a light source to one of the optical gratings through a lens, and the rays, which have passed through the optical grating, further passes through the other of the optical gratings and reaches a receptor through a lens desposed on the other side.
In consequence, the rays from the light source are necessitated to pass through the two optical gratings, mixed with complex diffracted rays on the way, attenuated due to reflection and refraction of the surface of glass as being the base member of the optical grating, and further, absorption in the glass. As the result, signals obtained by a receptor, including noises, are necessitated to be weak. Further, the provisions of the light source, the lens and the receptor have necessarily resulted in a large-sized encoder.
There have also been the reflection type photoelectrical encoders in which the rays are caused to obliquely incide between the two optical gratings. The encoders of the type described are apt to a great loss in light quantity due to the diffraction, scattering, reflection and the like, the oblique mounting of the light source and the receptor have made it necessary to adopt construction of the encoder being complex and not satisfactorily compact.
In order to obviate the above-described disadvatages of the prior art, the present applicant has proposed the photoelectrical encoder wherein, in one of the optical gratings, a semiconductor base member is provided thereon at regular pitches with narrow belt-shaped conductive (contrary to the semiconductor base member) semiconductor layers, onto which the rays, which have transmitted through the other of the optical gratings are radiated, whereby outputs are obtained from the semiconductor base member and the semiconductor layers.
Such improvements for the compactness of the encoder and the working efficiency have been introduced in the above-described proposal that the lens on the side of the receptor being dispensed with, allowing the rays from the light source to pass through only one of the optical gratings and eliminating the space between the second optical gratings and the receptor.
As against the aforesaid proposal, there has further been proposed a photoelectrical encoder wherein, in order to obviate or decrease the resistance of slits for the improvements in the high-frequency characteristics of the outputs from slit-shaped light receiving elements consisting of the semiconductor base member and the semiconductor layers, the whole surfaces of the light receiving elements are coated with a transparent conductive material to put together the outputs.
There has still further been proposed a photoelectrical encoder wherein a continually flat semiconductor layer is provided thereon with slits having an opaque film, whereby the high-frequency characteristics is improved and the production is facilitated.
There has yet further been proposed a photoelectrical encoder wherein the semiconductor base member and the semiconductor layer are made of MOS semiconductor and the slits having the opaque film are made of a metal portion in the MOS semiconductor.
Notwithstanding, scales of the aforesaid photoelectrical encoders are not satisfactorily rendered compact, and, in the case of the scale made of MOS semiconductor for example, a silicon crystal used as the material is high in cost and cannot formed into an elongate form, thus presenting difficult problems from the economic and technical viewpoints. This is especially true of the case of applying the same to the main scale.
In general, the reflection type photoelectrical encoder is more compact in construction than the transmitting type photoelectrical encoder. In the case of the reflection type encoder, the rays for being radiated onto a relection scale must be caused to obliquely incide. Because of this, there are presented such disadvantages that the loss in light due to the diffraction, scattering, reflection and the like is great, a light emitting portion and light receiving portions are obliquely mounted, thus resulting in complicated construction.